If you don’t plan to run Reason Essentials, just launch the host application as usual. We recommend that you then also deactivate all ReWire channels if required (see the relevant section for your program, below). But this is not completely critical; ReWire does not use up very much processing power when it isn’t used.
You may get a warning message in the host application, regarding ReWire, but you can safely ignore it. Please also note that the two programs now compete for system resources such as audio cards, just as when running either with other, non-ReWire, audio applications.